KR20100005246A - Process for the production of polypropylene articles with increased response to surface energy increasing treatment - Google Patents

Abstract

The present invention relates to a process for the production of polypropylene articles with improved response to a surface energy increasing treatment, wherein the polypropylene comprises a metallocene-catalyzed polyethylene. The present invention further relates to the use of metallocene-catalyzed polyethylene as an additive for improving the response of polypropylene to surface energy increasing treatments.

Description

PROCESS FOR THE PRODUCTION OF POLYPROPYLENE ARTICLES WITH INCREASED RESPONSE TO SURFACE ENERGY INCREASING TREATMENT}

The present invention relates to a process for producing a polypropylene article with improved response to surface energy increasing treatment, wherein the polypropylene comprises metallocene-catalyzed polyethylene. The invention also relates to the use of metallocene-catalyzed polyethylene as an additive for improving the response of polypropylene to surface energy increasing treatment.

Polypropylene is one of the most widely used industrial polymers. Its mechanical, chemical and processing properties make it the material of choice in a variety of applications, but its chemical inertness and low surface energy cause problems in applications requiring printing, coating, bonding or bonding with other components. do. Therefore, for these applications, it is necessary to apply polypropylene to surface-modifying treatments that increase surface energy. In printing applications, the surface energy needs to be increased from about 30 mN / m to about 38 mN / m for solvent-based inks and about 45 mN / m for water-based inks. Increasing the surface energy of polypropylene is particularly difficult because the energy required to increase surface energy is much greater than other polymers.

Methods of increasing the surface energy of polypropylene include chemical treatment, flame treatment and Corona treatment. For safety and environmental reasons, chemical treatments using strong oxidants such as chromic acid are increasingly used. In flame-treatment, the polypropylene surface is treated with an oxidizing gas flame. In corona-treatment, the polypropylene surface is treated with electrically ionized air. All methods have in common that an oxidized center occurs, which facilitates the attachment of inks and the like.

The main disadvantage of flame- and corona-treatment is that the treatment effect is quickly lost. Within one week of treating polypropylene, a decrease of 3 mN / m can occur. Therefore, in many cases the treated polypropylene requires a "refresher" treatment before further deformation.

WO 00/54968 includes a central layer comprising an ordered polypropylene, and an ethylene or propylene homopolymer, an ethylene copolymer, a terpolymer containing propylene, ethylene and butene-1 as comonomers, or blends thereof. An oriented multilayer film comprising at least one additional layer adjacent to the central layer is described. The polymer of the additional layer can be produced by Ziegler-Natta catalysis or metallocene catalysis. Oriented multilayer films can be applied to treatments that increase surface energy, such as, for example, corona-treatment. However, WO 00/54968 does not describe how polypropylene's response to corona-treatment can be improved.

WO 2004/098868 includes polypropylene, fillers and metallocene-catalyzed polyethylenes (metallocene-catalyzed polyethylenes have a density in the range from 0.850 g / cm 3 to 0.925 g / cm 3 and are therefore low density polyethylene). Multilayer films are described which may have a peel layer. Multilayer films can be applied to surface-energy enhancement treatments, such as corona-treatment, to improve printability. However, WO 2004/098868 does not describe how the sensitivity of polypropylene to corona-treatment can be increased.

WO 00/58090 discloses (a) a core layer comprising a propylene polymer, (b) a raised outer layer on one side of the center layer, and (c) an addition on the face of the center layer opposite the raised outer layer. Multilayer films are described that include conventional outer layers. The polymer of the raised outer layer (b) is ethylene-propylene-butylene (EPB) terpolymer, ethylene-propylene (EP) copolymer, metallocene-catalyzed polyethylene, ordered polypropylene, propylene-butylene Random copolymers, and blends of any of the above components (with or without isotropic polypropylene homopolymer). The raised outer layer (b) can be flame-treated or Corona-treated. However, WO 00/58090 does not describe how the performance of polypropylene for corona treatment can be improved.

Therefore, there is a great interest in the industry to facilitate the surface modification of polypropylene.

Brief Description of the Invention

Applicants have now discovered a method that enables the production of polypropylene articles with improved response to surface energy increasing treatment.

Therefore, the present invention provides a method of making a polypropylene article with improved response to surface energy increasing treatment, comprising:

(a) providing a polypropylene comprising a metallocene-catalyzed polyethylene,

(b) then forming an article, and

(c) subjecting the article to a treatment that increases surface energy.

The present invention also relates to the use of metallocene-catalyzed polyethylene as surface energy increasing additive.

Detailed description of the invention

The polypropylene used in the present invention may be a homopolymer, a random copolymer or a heterophasic copolymer. Homopolymers and random copolymers are preferred polypropylenes. Random copolymers are the most preferred polypropylenes. Random and heterophasic copolymers are copolymers of propylene and one or more comonomers, which comonomers are ethylene and C ₄ -C ₁₀ alpha-olefins such as 1-butene, 1-pentene, 1-hexene, 1- It is selected from the group which consists of octene.

The random copolymer comprises at least 6 wt%, preferably at most 5 wt%, most preferably at most 4 wt% of one or more comonomers. It comprises at least 0.1% by weight, more preferably at least 0.5% by weight, even more preferably at least 1% by weight, most preferably at least 2% by weight of one or more comonomers. Preferably, the random copolymer is a copolymer of propylene and ethylene.

Heterophasic copolymers include a propylene homopolymer or random copolymer as defined above, and a matrix consisting of a rubbery phase. The heterophasic copolymer may comprise from 5% by weight to 35% by weight of the rubber phase. Preferably, the heterophasic copolymer is a copolymer of propylene and ethylene. Its ethylene content is in the range of 4% to 15% by weight. Preferably, the rubber phase is ethylene propylene rubber.

The polypropylenes used in the present invention can be prepared by polymerizing propylene with one or more optional comonomers according to methods well known to those skilled in the art.

The polypropylene used in the present invention has a melt flow index (measured under conditions L, a temperature of 230 ° C. and a load of 2.16 kg, according to ISO 1133) in the range of 0.1 dg / min to 100 dg / min. One skilled in the art recognizes that the suitable melt flow range of the polypropylene depends on each method of forming the article. Therefore, the preferred melt flow index range for Injection Stretch Blow Molding (ISBM) is 1.5 dg / min to 30 dg / min. The preferred melt flow index range for cast film extrusion is from 3.0 dg / min to 15 dg / min. The preferred melt flow index range for blown film extrusion is from 0.3 dg / min to 3.0 dg / min. Preferred melt flow index ranges for blow molding range from 0.3 dg / min to 3.0 dg / min. The preferred range for sheet extrusion is from 2.0 dg / min to 10 dg / min. The preferred range for injection molding is 10 dg / min to 100 dg / min.

The polypropylene of the present invention comprises at least 1% by weight, preferably at least 2% by weight, of metallocene-catalyzed polyethylene, ie polyethylene produced using a metallocene-based catalyst system. The polypropylene comprises up to 20% by weight, preferably up to 15% by weight and most preferably up to 10% by weight of metallocene polyethylene.

Polypropylenes comprising metallocene-catalyzed polyethylenes may be prepared by dry-mixing or mixing. It is also possible to carry out the mixing during the pelletization step in the polypropylene production plant.

Blends of polypropylene and metallocene-catalyzed polyethylene are known from WO 2005/005143, for example, for improving the impact performance of containers. However, WO 2005/005143 does not mention the use of such compositions for improving the response to surface energy increasing treatment.

WO 00/54968, already mentioned, does not directly describe blends of polypropylene and metallocene-catalyzed polyethylene for use in corona-treatment. Neither WO 00/54968 nor WO 2004/098868 describe that the response of polypropylene to corona-treatment can be improved by the addition of metallocene-catalyzed polyethylene. WO 00/58090 already mentioned does not describe the improvement of corona-treatment of polypropylene when a certain amount of metallocene-catalyzed polyethylene is added to the polypropylene.

The metallocene-catalyzed polyethylene may be a homopolymer of ethylene or a copolymer of ethylene and one or more comonomers, said comonomers being C ₃ to C ₁₀ alpha-olefins such as 1-butene, 1-pentene, 1- Hexene, 1-octene, 1-methylpentene, 1-butene and 1-hexene are preferred comonomers and 1-hexene is the most preferred comonomer.

Metallocene-based catalyst systems used in the preparation of metallocene-catalyzed polyethylenes include metallocenes, supports and activators. Such metallocene-based catalyst systems are known to those skilled in the art and do not require detailed description.

For the purposes of the present invention, any known metallocene may be used, for example bis (n-butylcyclopentadienyl) zirconium dichloride. However, the formula

R "(lnd) ₂ MQ _q

(Wherein lnd is substituted or unsubstituted indenyl or tetrahydroindenyl, R ″ is a structural crosslink that gives rigidity between two indenyl, C ₁ -C ₄ alkylene radical, dialkyl germanium or Silicon or siloxane, or alkyl phosphine or amine radicals, preferably Me ₂ C, ethylene, Ph ₂ C or Me ₂ Si; M is a 4, 5 or 6 transition metal; Q is a hydrocarbyl radical, such as Aryl, alkyl, alkenyl, alkylaryl, or an aryl alkyl radical having 1 to 20 carbon atoms, a hydrocarboxy radical having 1 to 20 carbon atoms or halogen, and may be the same or different from each other; q is a valency of M-2) of Preference is given to using metallocenes.

Preferably, indenyl or tetrahydroindenyl, if substituted, are symmetrically substituted at positions 2 and / or 4, more preferably unsubstituted.

Such metallocene components are described in WO 96/35729. Most preferred metallocene is ethylenebis (4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride.

The molecular weight distribution of the metallocene-catalyzed polyethylene can be defined by a parameter known as the dispersion index D which is the ratio between the weight average molecular weight (M _w ) and the number average molecular weight (M _n ). Dispersion index D consists of a measure of the molecular weight distribution width. In the metallocene-catalyzed polyethylene of the present invention, the dispersion index D is 2 to 7, preferably 2 to 5.

The metallocene-catalyzed polyethylene used in the present invention has a melt flow index in the range of 0.1 dg / min to 100 dg / min (measured under condition D, temperature of 190 ° C. and load of 2.16 kg, according to ISO 1133). Has Those skilled in the art recognize that the suitable melt flow range of polyethylene depends on the respective method of forming the article. Therefore, the preferred melt flow index range for injection stretch blow molding (ISBM) is 1.5 dg / min to 30 dg / min. The preferred melt flow index range for cast film extrusion is from 3.0 dg / min to 15 dg / min. The preferred melt flow index range for blown film extrusion is from 0.3 dg / min to 3.0 dg / min. Preferred melt flow index ranges for blow molding range from 0.3 dg / min to 3.0 dg / min. The preferred range for sheet extrusion is from 2.0 dg / min to 10 dg / min. The preferred range for injection molding is 10 dg / min to 100 dg / min.

The metallocene-catalyzed polyethylene used in the present invention is at least 0.920 g / cm 3, preferably at least 0.925 g / cm 3, more preferably at least 0.927 g / cm 3, even more preferably at least 0.930 g / cm 3, most Preferably it has a density of at least 0.932 g / cm 3. It has a density of 0.965 g / cm 3 or less, preferably 0.955 g / cm 3 or less, more preferably 0.950 g / cm 3 or less, even more preferably 0.945 g / cm 3 or less, most preferably 0.940 g / cm 3 or less. . Density is measured at 23 ° C. according to the method described in ASTM D 1505.

Without being bound by theory, when measured at high temperatures or at low equivalent Short Chain Branches (SCB) content, the amount of crystallization appears to play an important role in the compatibility between polypropylene and metallocene-catalyzed polyethylene. Is considered. The amount of crystallization as a function of short chain branching is measured by the Stepwise Isothermal Segregation Technique (SIST). In this technique, the sample is heated from room temperature (25 ° C.) to 220 ° C. at a rate of 200 ° C./min. This is kept at 220 ° C. for 5 minutes. It is then lowered to a temperature of 140 ° C. at a rate of 20 ° C./min and held at this temperature for 40 minutes. The temperature is then lowered stepwise at 5 ° C. at a rate of 20 ° C./min and held for 40 minutes in each step until a temperature of 90 ° C. is reached. It is then cooled to 25 ° C. at the fastest cooling rate and held at 25 ° C. for 3 minutes. It is then reheated from 25 ° C. to 180 ° C. at a rate of 5 ° C./min. % Crystallization is described in Satoru Hosada in Polymer Journal, vol. 20, p. 383, 1988] is deduced from the curve representing the SCB as a function of the melting temperature. In the metallocene-catalyzed polyethylene used in the present invention, the% crystallization corresponding to the chain having less than 10 SCB for 1000 carbon atoms is at least 4%, preferably at least 7%.

As well as polypropylene, metallocene-catalyzed polyethylenes all contain additives such as, for example, antioxidants, light stabilizers, acid scavengers, lubricants, antistatic additives, nucleating agents / cleaning agents, colorants, slip agents. It may contain. An overview of these additives is provided in the Plastics Additives Handbook, ed. H. Zweifel, 5 ^th edition, 2001, Hanser Publishers.

With polypropylene comprising the metallocene-catalyzed polyethylene according to the invention, the product is for example injection molded, blow molded, injection stretch blow molded (ISBM), cast or blown film extrusion, fiber or nonwoven extrusion , By any known modification method such as sheet extrusion.

After its preparation, polypropylene products are subjected to surface energy increasing treatments such as chemical treatment, flame-treatment and corona-treatment. Preferred methods are flame- and corona-treatment. The most preferred method is corona-treatment.

For corona-treatment, the polypropylene article typically passes between two electrodes having a voltage in the range of about 10 kV to about 20 kV. At this voltage, a spray or corona discharge can occur, which then causes the air on top of the article to ionize and react with the surface molecules of the polypropylene article, forming a polar center.

For sparking to polar flames, a voltage is applied between the burner acting as the cathode and the chill roll in another element, for example film or sheet extrusion. The applied voltage ranges from about 0.5 kV to about 3 kV. This accelerates the ionized atoms, which strike the polypropylene surface at a high rate and then break the bond on the surface of the polypropylene article. As a result, a polar center is formed.

Polypropylene, including metallocene-catalyzed polyethylene, is found to be more responsive to surface energy increasing treatment. Very surprisingly, the polypropylenes of the present invention have also been found to slowly reduce the effect of surface-modifying treatment. Compared to articles with improved surface energy, made of pure polypropylene, polypropylene articles comprising metallocene-catalyzed polyethylenes are further modified, eg, prior to printing, without the need to apply a "refresh agent" treatment. Can be stored for a longer time.

Therefore, metallocene-catalyzed polyethylenes act as additives in polypropylene to improve response to surface energy increasing treatments such as chemical treatment, flame-treatment and corona-treatment. Preferred methods are flame- and corona-treatment. The most preferred method is corona-treatment.

Claims (13)

A method of making a polypropylene article having improved response to surface energy increasing treatment, comprising: (a) providing a polypropylene comprising a metallocene-catalyzed polyethylene, (b) then forming an article, and (c) subjecting the article to a treatment that increases surface energy, Wherein the polypropylene provided in step (a) comprises 1% to 20% by weight of metallocene-catalyzed polyethylene. The process of claim 1 wherein the polypropylene comprises from 2% to 15% by weight of metallocene-catalyzed polyethylene. The method of claim 1 or 2, wherein the density of the metallocene-catalyzed polyethylene is at least 0.920 g / cm 3, preferably at least 0.925 g / cm 3, 0.927 g / cm as measured at 23 ° C. according to ASTM D 1505. At least cm 3, at least 0.930 g / cm 3 or at least 0.932 g / cm 3. The density of the metallocene-catalyzed polyethylene according to claim 1, wherein the density of the metallocene-catalyzed polyethylene is 0.965 g / cm 3 or less, preferably 0.955 g / cm 3 or less as measured at 23 ° C. according to ASTM D 1505. , 0.950 g / cm 3 or less, 0.945 g / cm 3 or less, or 0.940 g / cm 3 or less. 5. The% crystallization according to claim 1, wherein the metallocene-catalyzed polyethylene has a% crystallization of at least 4%, preferably 7, corresponding to a chain having less than 10 short chain branches per 1000 carbon atoms. Way more than%. The method of claim 1, wherein the surface energy increasing treatment of step (c) is corona-treated or flame-treated. The process according to any one of claims 1 to 6, wherein in step (b) the polypropylene article is selected from the group consisting of injection stretch blow molding, flat film extrusion, blown film extrusion, sheet extrusion and injection molding. Formed by. Use of metallocene-catalyzed polyethylene as an additive for improving the response of polypropylene to surface energy increasing treatment. The use of a metallocene-catalyzed polyethylene according to claim 8, wherein the metallocene-catalyzed polyethylene is added to the polypropylene in an amount of 1% to 20% by weight. 10. The method according to claim 8 or 9, wherein the density of the metallocene-catalyzed polyethylene is at least 0.920 g / cm 3, preferably at least 0.925 g / cm 3, 0.927 g / cm as measured at 23 ° C. according to ASTM D 1505. Use of a metallocene-catalyzed polyethylene of at least cm 3, at least 0.930 g / cm 3 or at least 0.932 g / cm 3. The method of claim 8, wherein the density of the metallocene-catalyzed polyethylene is 0.965 g / cm 3 or less, preferably 0.955 g / cm 3 or less, as measured at 23 ° C. according to ASTM D 1505. , Up to 0.950 g / cm 3, up to 0.945 g / cm 3 or up to 0.940 g / cm 3. The method according to claim 8, wherein the metallocene-catalyzed polyethylene has a% crystallization of at least 4%, preferably 7, corresponding to a chain having less than 10 short chain branches per 1000 carbon atoms. Use of metallocene-catalyzed polyethylene that is at least%. A polypropylene article made according to the method of claim 1.